1. Field of the Invention
The disclosure relates to a vapor deposition reactor and a method for forming a thin film using the same.
2. Description of the Related Art
In general, a showerhead-type reactor is used in chemical vapor deposition (CVD) for injecting a precursor. In the showerhead-type reactor deposition is performed by mixing a source precursor and a reactant precursor within the interior of a showerhead and then spraying the mixed precursors onto a substrate. On the other hand, in a reactor for atomic layer deposition (ALD), a source precursor and a reactant precursor are alternately sprayed so that they are not mixed with each other. Based on the direction of the precursor spray, reactors are divided into (i) a cross-flow or traveling-wave type reactor and (ii) a type of reactor that injects the precursor vertically to the surface of the substrate. The cross-flow or traveling-wave type reactor injects a precursor in a direction parallel to a surface of a substrate surface for deposition of the precursor.
The ALD uses the bonding force of a chemisorbed layer that is different from the bonding force of a physisorbed layer. In the ALD, a precursor is absorbed into the surface of a substrate and then purged with an inert gas. As a result, physisorbed molecules of the precursor (bonded by the Van der Waals force) are desorbed from the substrate. However, chemisorbed molecules of the precursor are covalently bonded, and hence, these molecules are strongly adsorbed in the substrate. Hence, the chemisorbed molecules are not desorbed from the substrate. The ALD is performed using the properties that the chemisorbed molecules of the precursor (adsorbed in the substrate) react and/or replace a reactant precursor.
More specifically, a source precursor is injected into a chamber so that the source precursor is excessively adsorbed on a substrate. Then, the excessive precursor or physisorbed molecules are removed by injecting a purge gas and/or pumping the chamber, causing only chemisorbed molecules to remain on the substrate. The chemisorbed molecules results in a mono molecule layer. Subsequently, a reactant precursor (or replacement agent) is injected into the chamber. Then, the excessive precursor or physisorbed molecules are removed by injecting the purge gas and/or pumping the chamber, obtaining a final atomic layer.
In the ALD, a basic unit consisting of these four processes is usually referred to as a cycle. If a chemisorbed layer in a saturation state is obtained, a deposition velocity of about 1 Å per cycle is obtained. However, when a precursor is not adsorbed on the substrate in the saturation state, a deposition velocity is slower than about 1 Å per cycle. If the physisorbed molecule layer is not completely removed but a portion of the physisorbed molecule layer remains on the substrate, the deposition velocity is increased.
In the ALD, one atomic monolayer is usually formed per cycle. In the ALD, a source precursor, a reactant precursor and a purge gas are repeatedly injected into a chamber, and a valve and a pump are used for exhaustion. For example, the ALD technique has been disclosed in U.S. Pat. Nos. 7,422,636, 7,402,210, 6,511,539 and 6,820,570, which are incorporated by reference herein in their entirety.
If precursors injected into a chamber in each process remain in the chamber, a vapor phase reaction (referred to as a CVD reaction) occurs through the reaction of a source precursor and a reactant precursor. Therefore, only a valve for ALD operated at a high speed is necessary to perform the ALD, and purging and/or pumping must be performed so that no precursor remains in the chamber. At this time, the valve used for ALD requires an extended operation times. For example, operation times of more than 103 for each of the processes of injecting the source precursor, purging, injecting the reactant precursor, purging and the like are usually necessary to deposit an atomic layer with a thickness of 100 nm. As a result, the lifetime of the valve is shortened, and its reliability is decreased. As the number of operation times of the valve operated at a high speed is increased, problems related to the lifetime of the valve occur, such as erroneous operations or particles.
However, when a thin film is formed using the ALD, it is important to form the thin film having uniform characteristics (i.e., physical, chemical and electrical characteristics) required to satisfy requirements of a device. To this end, it is necessary that times at which the respective source and reactant precursors reach a substrate be identical in the injection of the source and the reactant precursor. In the cross-flow or traveling-wave type reactor in which precursors used for the ALD are injected parallel to a substrate, an adsorption phenomenon is gradually performed while the substrate is passes from the side adjacent to an injection portion of the precursors and to the side of an exhaust portion. Therefore, the adsorption phenomenon is represented by a function of time. Particularly, for a large-area substrate, such a phenomenon becomes more pronounced, and therefore, the composition, thickness or property of the thin film varies depending on each portion of the substrate. Particularly, the compositions, thicknesses or properties of the thin films respectively positioned at the injection and exhaust portions are different from each other.
In the reactor for receiving the precursors, the precursors are injected in a direction vertical to the substrate to avoid such a problem. However, when the distance between the injection portion (typically, showerhead) of the precursors and the substrate is short, the thickness of the thin film is increased or decreased by the proximity phenomenon in the vicinity of a hole of the showerhead through which the precursors are injected, and therefore, an irregular thin film having a hole pattern of the showerhead is obtained. Accordingly, the distance between the injection portion and the substrate need to be sufficiently large. As a result, the space portion of the chamber is increased. Also, a large amount of precursor is required because a sufficient amount of precursor is necessarily filled in the interior of the chamber for the purpose of saturation adsorption of precursors on a surface of the substrate. Also, the source precursors and the reactant precursors do not come in contact with each other so as to avoid a CVD reaction. Therefore, much time is taken to perform sufficient purging and/or pumping to prevent the source precursors or reactant precursors from remaining in the chamber. In addition, since the source precursors and the reactant precursors are exhausted through the same exhaust line, a reactant byproduct (e.g., powder, gum or the like) is produced by the reaction of these precursors. Therefore, the reliability, durability and economy of the device are decreased as well as yielding thinner film.
In U.S. Pat. No. 6,821,563, for example, gas steam flowed through a plurality of gas ports is supplied to a substrate, and purge and pump ports are installed adjacent to each other so that the ALD is performed by purging and pumping while consecutively injecting precursors. However, partitions for isolating or separating the ports from each other are installed, and pumping ports are positioned at both sides of each of the partitions, respectively. Hence, its structure is complicated. In addition, since the partitions serve as only physical barriers for isolating the ports from each other, there is a structural limitation in that pumping ports are necessarily positioned at both sides (or left and right sides) of each of the ports through which the precursors are injected or purged.